Browsing by Author "Gichumbi, J. M."

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Antibacterial and Antifungal activities of Novel hydroxytriazenes.
(2012-04-02) Ombaka, A.O *; Muguna, A. T.; Gichumbi, J. M.
In a search for new leads potent antimicrobial agents, an array of novel hydroxytriazenes i-xi were synthesized and characterized through their melting point, crystal shape, colour and elemental analysis. In vitro microbiological evaluations were carried out for all the synthesized compounds against both bacterial and fungi using the turbidimetric method. The reagent number x and xi showed significant antibacterial activities against two gram positive [Streptococcus feacalis, Staphylococcus aureus, penicillin resistance (2500 units)]. All synthesized hydroxytriazenes except reagent number viii showed antifungal activities against five fungi [Candida albicans, Cryptococcus neoformans, Sporotrichum schenckii, Trichophyton mantagrophytes, Aspergillus fumigatus}. The minimum inhibitory concentration (mic) values against these bacteria and fungi ranged from <12.5 to 50 μg/ml. Some hydroxytriazenes (x, xi) showed an unusual combined antibacterial and antifungal action, which suggest that hydroxytriazenes revealed a wide range of antimicrobial activity.
Antibacterial and antifungal activities of novel hydro
(2012) Ombaka, A. O.*; Muguna, A. T.; Gichumbi, J. M.
In a search for new leads potent antimicrobial agents, an array of novel hydroxytriazenes i-xi were synthesized and characterized through their melting point, crystal shape, colour and elemental analysis. In vitro microbiological evaluations were carried out for all the synthesized compounds against both bacterial and fungi using the turbidimetric method. The reagent number x and xi showed significant antibacterial activities against two gram positive [Streptococcus feacalis, Staphylococcus aureus, penicillin resistance (2500 units)]. All synthesized hydroxytriazenes except reagent number viii showed antifungal activities against five fungi [Candida albicans, Cryptococcus neoformans, Sporotrichum schenckii, Trichophyton mantagrophytes, Aspergillus fumigatus}. The minimum inhibitory concentration (mic) values against these bacteria and fungi ranged from <12.5 to 50 μg/ml. Some hydroxytriazenes (x, xi) showed an unusual combined antibacterial and antifungal action, which suggest that hydroxytriazenes revealed a wide range of antimicrobial activity.
Antibacterial and antifungal activities of novel hydroxytriazenes
(2012-04-02) Ombaka, A. O.*; Muguna, A. T.; Gichumbi, J. M.
In a search for new leads potent antimicrobial agents, an array of novel hydroxytriazenes i-xi were synthesized and characterized through their melting point, crystal shape, colour and elemental analysis. In vitro microbiological evaluations were carried out for all the synthesized compounds against both bacterial and fungi using the turbidimetric method. The reagent number x and xi showed significant antibacterial activities against two gram positive [Streptococcus feacalis, Staphylococcus aureus, penicillin resistance (2500 units)]. All synthesized hydroxytriazenes except reagent number viii showed antifungal activities against five fungi [Candida albicans, Cryptococcus neoformans, Sporotrichum schenckii, Trichophyton mantagrophytes, Aspergillus fumigatus}. The minimum inhibitory concentration (mic) values against these bacteria and fungi ranged from < 12.5 to 50 µg/ml. Some hydroxytriazenes (x, xi) showed an unusual combined antibacterial and antifungal action, which suggest that hydroxytriazenes revealed a wide range of antimicrobial activity.
Characterization of clays from Tharaka-Nithi County in Kenya for industrial and agricultural applications
(2015) Njoka, E. N.; Ombaka, O.; Gichumbi, J. M.; Kibaara, D. I.; Nderi, O. M.
Clay samples from Tharaka-Nithi County in Kenya were characterized by hydrometer, X-ray fluorescence spectroscopy (XRF), atomic absorption spectroscopy (AAS), TGA, scanning electron microscopy (SEM) and powder diffraction (XRD) methods. The F-test and t-test were used to interpret the results. The major oxides present were Al2O3, SiO2 and the minor ones were CaO, TiO2, MnO, Fe2O3, K2O, MgO and Na2O. The values of SiO2 were greater than those of Al2O3, indicating that the samples were of clay minerals. The clay minerals with low cation exchange capacity (CEC) were present in the samples. The Atterberg limits showed that the inorganic clays of either low or intermediate plasticity having low contents of organic matter were present in the samples. The analysis further showed the availability of essential elements necessary for plant growth. The TGA analysis indicated that the decomposition of clay samples occurred in four steps. The scanning electron microscope photographs revealed that the samples contained a mixture of minerals of morphologies with crystallinity, high porosity and unstable under the electron beam. The major impurity in the clay is quartz, ranging from 22.6-31.9%. Albite is the most dominant component in the clay minerals contributing to 30.3 to 44.1%. The clay from the study area can be used as agro mineral additive to enhance soil fertility for crop production, a fluxing agent in ceramics and glass applications and also as functional fillers in the paint, plastic, rubber and adhesive industries after beneficiation.
Crystal structure of chlorido-(η6- toluene)(2,2′-bipyridine-κ2N,N′)ruthenium(II) hexafluorophosphate, C17H16ClN2RuPF6
(De Gruyter, 2022) Gichumbi, J. M.; Friedrich, H. B.; Zamisa, S. J.
C17H16ClN2RuPF6, monoclinic, P21/c (no. 14), a = 14.4426(9) Å, b = 8.3311(5) Å, c = 16.413(1) Å, β = 109.2690°, V = 1864.2(2) Å3, Z = 4, Rgt(F ) = 0.0309, wRref(F 2) = 0.0697, T = 173 K.
EVALUATION OF ANTIMICROBIAL ACTIVITIES OF Tithoniadiversifolia AND Kigeliaafricana AGAINST TOMATO FUSARIUM WILT PATHOGEN (FusariumoxysporumLycopersci)
(Chuka University, 2021) Awere, C. A.; Githae, E. W.; Gichumbi, J. M.
Fusarium wilt disease caused by the soil-borne fungusFusariumoxysporum Schlechttheisaserious threat to tomato production worldwide. Chemical and cultural methods of management used are either ineffective or toxic to the environment. Plant secondary metabolites; therefore, pose a possible alternative because they are environmentally friendly and have minimal effect on non-target organisms. This study screened phytochemical compounds of two plants; Tithonia diversifolia (Hemsl.) A. Gray and Kigelia africana (Lam.) Benth and assessed their potency in controlling plant fungal pathogen F. oxysporum, a causal agent of Fusarium wilt disease in tomatoes. Leaf extractsof T. diversifolia and fruit extract of K. africana were concentrated in water and screened for phytochemical contents using standard procedures. Concentrations used were25g/L,50g/Land100g/Ltosockthedisc. Fusarium oxysporum was isolated from infected soil using potato dextrose media, Antifungal activity was evaluated by measuring the zone of inhibition against the test organism. The results showed that the mean inhibitory zones were highest at 100g/l in both plants, although K. africana fruit extract portrayed the highest inhibitoryactivity compared to Tithonia africana. The effect of the plant extracts and the negative control was statistically significant (p<0.05). This study indicates that K. africana and T. diversifolia possess the antifungal activity and can be used as a broad- spectrum fungicide against F. oxysporum. These plant extracts may provide an effective measure for the management of Fusarium wilt of tomatoes that may form an integral part of integrated management and it also has prospect as an alternative to reliance only on fungicides.
Investigation Of Physicochemical and Bacteriological Characteristics Of Water Samples From Irigu River Meru South, Kenya
(2012-11) Ombaka, O.; Gichumbi, J. M.
Physicochemical and bacteriological parameter levels of river Irigu were investigated during wet and dry season in order to assess the degree of pollution .The results obtained were compared with WHO standards for drinking water. The physicochemical parameters analyzed were in compliance with the WHO standards except pH, turbidity, phosphorous, iron, manganese, Pb and Al. The values of MPN of coliform organisms /100 ml and E.Coli/100 ml were above the recommended values by WHO. The water from Irigu is not safe for domestic use and requires purification. There is need for awareness programs to educate local villagers to safeguard the river.
Phthalate Levels in Wastewater Treatment Plants of Lake Victoria Basin
(Science and Education Publishing, 2021) Onchiri, R.; Mayaka, A.; Majanga, A.; Orata, F.; Getenga, Z. M.; Gichumbi, J. M.; Ongulu, R.
Phthalates are examples of EDCs, which have been used as plasticizers for longtime worldwide. However, their occurrence in these environments causes adverse effects such as congenital anomalies, endocrine disruption and chronic toxicity. Wastewater is the source of these phthalates in the environment. The main aim of this study was to determine the levels of dimethyl phthalate (DMP), benzyl butyl phthalate (BBP) and bis (2-ethylhexyl) phthalate (BEHP) in wastewater sampled from wastewater treatment plants (WWTPs) of Nyalenda, Homabay and Kisii, in Kenya during wet and dry seasons. Thermos Scientific Dionex UltiMateTM 3000 HPLC system was used to analyze the residue levels at 0.004 and 0.005 mg/L limits of quantification during wet and dry seasons, respectively. Most sites sampled had detectable levels of DMP, BBP and BEHP. Higher concentrations were detected during wet season compared to dry season. At Nyalenda treatment plant, DMP was detected at 0.99 ± 0.0005 mg/L and 0.79 ± 0.0005 mg/L at the inlet sampling point during the wet and dry seasons, respectively. The concentrations detected were high at the inlet and lowest at the outlet sampling points. The residue levels obtained showed significant differences at 5% confidence limits with Zcalculated for DMP at Nyalenda, Homabay and Kisii WWTPs obtained as 0.2650, 0.2183 and 0.1983, respectively. These Z-score values (Zcalculated) were less than the critical value (Zcritical = 1.96). Similar observations were observed with BBP and BEHP
Spectrophotometric Determination of cobalt (II) in low concentrations using hydroxytriazene as selective chelating agents
(2011-12) Ombaka, Ochieng; Gichumbi, J. M.
The present work describes a selective, rapid and simple spectrophotometric method for the determination of cobalt (II) at trace levels using some selected hydroxytriazene. The method is based on the reaction of hydroxytriazene at pH 5.5 to 6.2, 6.0 to 6.8, 7.1 to 7.35, 7.3 to 7.9, 6.75 to 7.25 and 7.2 to 7.75 for hydroxytriazenes no (i), (ii), (iii), (iv), (v) and (vi) respectively and ethanol media with cobalt (II) to produce a highly absorbent yellow coloured chelate product with an absorption maximum at 393,397,417,406,410 and 412 nm for hydroxytriazenes no. (i), (ii), (iii), (iv), (v) and (vi), respectively. The reaction is instantaneous and the absorption remains stable for 24 Hrs. The average molar absorption coefficient were 1.1 x 104, 1.2 x 104,1.8 x 104, 2.5 x 104, 2.1 x 104, 1.9 x 104 mol-1 dm3 cm-1 for hydroxytriazene no (i), (ii), (iii), (iv), (v), (vi) respectively and Sandell’s sensitivity in ng/cm2 were 5.4, 4.9, 3.3, 2.4, 2.9 and 3.1 for hydroxytriazene no. (i), (ii), (iii), (iv), (v) and (vi), respectively. The stoichiometric composition of the chelate is 1:3 for hydroxytriazene no (i), (iv), (v), (vi), 1:2 for (ii) and 1:1 for (iii). A large excess of over 30 cations, anions and complexing agent do not interfere in the determination at equivalent amounts. The method was successfully used in Mussaenda arcu. The method has high precision and accuracy.
Spectrophotometric determination of cobalt (ii) in low concentrations using hydroxytriazene as selective chelating agents.
(2011-12) Ombaka, O. *; Gichumbi, J. M.
The present work describes a selective, rapid and simple spectrophotometric method for the determination of cobalt (II) at trace levels using some selected hydroxytriazene. The method is based on the reaction of hydroxytriazene at pH 5.5 to 6.2, 6.0 to 6.8, 7.1 to 7.35, 7.3 to 7.9, 6.75 to 7.25 and 7.2 to 7.75 for hydroxytriazenes no (i), (ii), (iii), (iv), (v) and (vi) respectively and ethanol media with cobalt (II) to produce a highly absorbent yellow coloured chelate product with an absorption maximum at 393,397,417,406,410 and 412 nm for hydroxytriazenes no. (i), (ii), (iii), (iv), (v) and (vi), respectively. The reaction is instantaneous and the absorption remains stable for 24 Hrs. The average molar absorption coefficient were 1.1 x 104 , 1.2 x 104 ,1.8 x 104 , 2.5 x 104 , 2.1 x 104 , 1.9 x 104 mol-1 dm3 cm-1 for hydroxytriazene no (i), (ii), (iii), (iv), (v), (vi) respectively and Sandell’s sensitivity in ng/cm2 were 5.4, 4.9, 3.3, 2.4, 2.9 and 3.1 for hydroxytriazene no. (i), (ii), (iii), (iv), (v) and (vi), respectively. The stoichiometric composition of the chelate is 1:3 for hydroxytriazene no (i), (iv), (v), (vi), 1:2 for (ii) and 1:1 for (iii). A large excess of over 30 cations, anions and complexing agent do not interfere in the determination at equivalent amounts. The method was successfully used in Mussaenda arcu. The method has high precision and accuracy.
Spectrophotometric Determination of Iron (III) by New Analytical Reagents Derived from Coupling Arylhydroxylamine and Aryldiazonium salt
(2012) Ombaka, O.; Gichumbi, J. M.
A highly sensitive and selective spectrophotometric method is developed for the determination of iron(III) in aqueous solution withhydroxytriazenes. In this work, the effect of pH variation, the composition of the complex of Fe3+ to hydroxytriazenes, precision, Sandell'ssensitivity and interference studies were investigated. This investigation was done under the optimum reaction conditions and otherimportant analytical parameters. Hydroxytriazenes reacts with the Fe3+ and forms coloured complexes. The Fe(III) complex is detected atλmax = 410 nm and pH range 3-4 for reagent no(i), 530 nm and 4-5 for reagent no (ii), 410 nm and 4.5 -5.5 for reagent (iii), 396 nm and 3.5-5.0 for reagent (iv), 467 nm and 2.5-3.5 for reagent no.(vi). Beer-Lambert's law is obeyed in the concentration range (1.0-5.0) × 10-5M,(1.5-9.0) × 10-5 M, (0.5-4.0) × 10-5 M, (0.3-1.8) × 10-5 M, (0.6-3.6) × 10-5 M, (2-12) × 10-5 M for nos. (i), (ii), (iii), (iv), (v), (vi)respectively. The molar ratio of Fe(III) to the hydroxytriazenes was found as 1:3. The limiting concentration for interference for 35diverse ions are reported. The standard deviation ranges between 0.019 to 0.088. The Sandell's sensitivity in ng/cm3 ranges between2.5.579 to 4.189. Reagent nos. (iii), (iv), (v), which were very sensitive were used to determine the level of iron in veg etable samples fromBaharini, Nakuru To wn and the results obtained were compared with those of atomic absorption spectrophotometer.
Spectrophotometric Determination of Iron(III) by New Analytical Reagents Derived from Coupling Arylhydroxylamine and Aryldiazonium Salt
(2012) Ombaka, O.*; Gichumbi, J. M.
A highly sensitive and selective spectrophotometric method is developed for the determination of iron(III) in aqueous solution with hydroxytriazenes. In this work, the effect of pH variation, the composition of the complex of Fe3+ to hydroxytriazenes, precision, Sandell's sensitivity and interference studies were investigated. This investigation was done under the optimum reaction conditions and other important analytical parameters. Hydroxytriazenes reacts with the Fe3+ and forms coloured complexes. The Fe(III) complex is detected at lmax = 410 nm and pH range 3-4 for reagent no(i), 530 nm and 4-5 for reagent no (ii), 410 nm and 4.5 -5.5 for reagent (iii), 396 nm and 3.5-5.0 for reagent (iv), 467 nm and 2.5-3.5 for reagent no.(vi). Beer-Lambert's law is obeyed in the concentration range (1.0-5.0) × 10-5 M,(1.5-9.0) × 10-5 M, (0.5-4.0) × 10-5 M, (0.3- 1.8) × 10-5 M, (0.6-3.6) × 10-5 M, (2-12) × 10-5 M for nos. (i), (ii), (iii), (iv), (v), (vi) respectively. The molar ratio of Fe(III) to the hydroxytriazenes was found as 1:3. The limiting concentration for interference for 35 diverse ions are reported. The standard deviation ranges between 0.019 to 0.088. The Sandell's sensitivity in ng/cm3 ranges between 2.5.579 to 4.189. Reagent nos. (iii), (iv), (v), which were very sensitive were used to determine the level of iron in vegetable samples from Baharini, Nakuru Town and the results obtained were compared with those of atomic absorption spectrophotometer.
Structural Properties of High Density Polyethylene Matrix Composites Reinforced with Open Air and Furnace Rice Husks Ash
(Academic Journals expand your Knowledge, 2021) Jonathan, M. K.; Osamong, G. A.; Butembu, S.; Kamweru, P. K.; Gichumbi, J. M.; Ndiritu, F. G.
In this work, rice husks ash (RHA) was introduced to pure and recycled high density polyethylene (HDPE) matrix, at varying ration (0-50%) to formulate rice husks ash High density polyethylene (RHA- HDPE) composite. RHA was obtained by burning fresh rice husks either by open-air burning (oRHA) or furnace calcination at 700°C (fRHA). The composite samples were made by melt-mixing the HDPE in an oven at a temperature of 150°C and adding different percentages of RHA in presence of maleic anhydride compatibilizer. Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) were carried out to determine the structural properties of the samples, and both suggest occurrence of composting chemical changes. For all RHA-HDPE samples, a broad band was noted between 970-070cm-1. This was highly contributed by the RHA and associated to Si-O-Si stretching modes. Other peaks are associated with Si-O-C interaction and O-Si-O bending vibrations in the samples. Scanning electron Microscopy (SEM) micrographs for HDPE indicated a smooth and uniform surface with a number of voids. On addition of RHA, the particles filled these voids making the sample surface rough. This roughness is seen to increase with increased percentage of RHA. The studies conclude that the cheaply obtained oRHA is as good as the fRHA in making RHA-HDPE composite.
Synthesis and insecticidal activities of some selected hydroxytriazenes. Journal of Environmental Chemistry and Ecotoxicology
(2011-10) Ombaka, O.; Gichumbi, J. M.
Eight hydroxytriazenes were synthesized and then subjected to spot tests. The composition of these hydroxytriazenes was analyzed using elemental analysis and their physical characteristics like melting point, crystal shape and colour were studied into details. The synthesized compounds were screened for their insecticidal activities against one day old male Drosophila melanogaster Meig (vinegar flies or fruit flies). Out of all the eight compounds screened, 3-hydroxy-3-m-tolyl-1-m-nitrophenyltriazene, 3- hydroxy-3-m-tolyl-1-p-methoxyphenyltriazene, 3-hydroxy-3-n-propyl-1-o-chlorophenyltriazene were the most active having LC50 values of 2.898, 3.898 and 1.812 ppm respectively. The least active compound is 3-hydroxy-3-m-tolyl-1-phenyltriazene having the value of 16.850 ppm. Heptachlor, a commercial product, had LC50 value of 1.570 ppm.